The present invention relates to a threaded implant intended to be screwed into bone, preferably into jawbone. In the screwed-in position, the implant is intended to support at least one spacer element. The implant has a socket arrangement which can cooperate on the one hand with a tool, for screwing it in, and on the other hand with the respective spacer element for screwing the latter on securely when the implant is in position. The invention also relates to an arrangement for a threaded implant of the said type and to a method for anchoring the implant in bone, preferably jawbone.
Implants of the type in question can be provided with a part which projects upwards from the upper contact surface of the implant which is designed with a wrench grip which can be used when the implant is being screwed into the hole made, for example, in jawbone. The upwardly projecting part can also receive and fix in position (inter alia in the direction of rotation) the spacer element and, if appropriate, any attachments on the latter. When the implant is being screwed in, relatively high torsion forces (for example torsion forces of the order of 50-100 Newton centimetres) may be needed, which in itself requires special measures to be taken in respect of the implant arrangement. When the implant is being screwed in or inserted, so-called fixture holders are often used which constitute a form of intermediate element which is screwed securely into or onto the implant, which, by virtue of this, can obtain a temporary tool attachment. An existing wrench grip according to the above, which is relatively low, does not then need to be used at least at high insertion forces and in positions where it is difficult to access and use the whole height of the low wrench grip. The wrench grip does not need to be used as tool attachment, and because the fixture holder is screwed securely into or onto the implant, a stable locking is obtained between the fixture holder and the wrench grip. The use of a fixture holder or intermediate element also has the advantage that the implant in question can be supported, that is to say secured, by the tightening machine used for inserting the implant, and this, together with an often more reliable and simpler tightening function, means that the technique using the fixture holder has hitherto predominated.
General reference is made to the PCT specifications WO 98/12982 and 98/31296.
Reference is also made to U.S. Pat. No. 4,960,381 which relates to a completely different type of implant, namely a type which does not have the part projecting upwards from the contact surface for the spacer attachment according to the above, and where instead the tool and spacer element sockets have been combined in a common position inside the implant.
In order to achieve high torque transmission forces despite the small dimensions which exist in connection with implants, it is advantageous if the orientation of the drive surfaces on the tool socket and corresponding acting surfaces on the tool are arranged such that they extend as radially as possible. Thus, for example, with two cooperating polygons, see the case above with a wrench grip on an upwardly projecting part, there is always a wedging effect between the tool and the socket, which means that the stability is limited, especially in the tool socket if, as in this case, for reasons of biocompatibility, it is not possible to use hard materials in the implant, that is to say in the tool socket. The invention aims to solve these problems among others.
There are also disadvantages with using the above-mentioned fixture holders. Among other things, extra torque is needed for mounting and dismantling the respective fixture holder onto or from the respective implant. In addition, the torque which can be transmitted between fixture/implant and fixture holder is limited. Exceeding the admissible torque can lead to great difficulties when removing the fixture holder, which means that the fixture has to be reversed. Another defect which can arise is that the hexagon of the fixture is so greatly deformed that attachment of the spacer is made difficult or impossible, which means that the insertion and healing procedure has to be repeated. The invention also solves this set of problems by taking the technique in new directions.
It is also essential to be able to use conventional and well proven spacer elements. It is of great importance that such spacer elements can be used for reasons of compatibility and that they are well proven. The invention also solves this problem.
The tool socket must be able to withstand high torques in accordance with the above, and at the same time it is advantageous that the tool and the tool socket are designed so that a support function is made possible. The invention solves this problem too.
Using an internal fixture socket as spacer attachment (cf. the US patent specification mentioned above) can cause problems in obtaining sufficient stability of the spacer element. A spacer element in this context must have a projecting part which cooperates with the recess in the fixture. To lock the spacer in place with a screw connection, this projecting part must be made hollow so that a screw can pass through. This greatly reduces the stability. If the spacers are intended to cooperate with the internal tool socket, the spacers become very expensive and difficult to manufacture. It is also difficult or quite impossible to manufacture, at a reasonable cost, a socket of this kind when the aim is to ensure that the outer surface of the spacer element will form a smooth transition from the implant. The invention solves this problem too, with the realization that the spacer socket as such does not have any requirements, or only minimum requirements, in respect of torque transmission and instead it essentially constitutes a positioning instrument.
When internal fixture sockets are used as spacer attachments, there is also the problem of achieving sufficient stability of the spacer elements. The invention solves this problem too.
The feature which can principally be regarded as characterizing a threaded implant in accordance with what has been stated above is that the socket arrangement comprises two geometrically separate sockets, of which the first socket can cooperate with the tool and the second socket permits rotational locking of the spacer element against the contact surface of the implant.
In further developments of the inventive concept, the second socket comprises a conventional socket of polygonal character, for example in the form of a hexagon socket. The latter can thus be assigned a spacer element in accordance with the previously used technique, and known and well proven spacer element structures can be used. The first socket can be arranged directly in the implant and thus not via the above-discussed fixture holders. The first socket can also be made internal and the second socket external. The second socket is arranged on a part projecting upwards from the contact surface of the implant, and the first socket is located essentially in the said projecting part, that is to say essentially above the contact surface of the implant. In an alternative embodiment, the first socket can be lowered inside the implant. The first socket can moreover comprise a number, preferably 4-6, of drive surfaces which can be acted on by the tool and which are arranged with salient or essentially radial extents. In further embodiments, the first socket can be arranged to accept a relatively high torque transmission force from the tool and at the same time have small dimensions in relation to the size of the implant and the internal socket. The first socket can also be arranged to permit a bearing function by means of the tool while it is being moved and used, for example a bearing function of the type which is described in the said WO 98/12982.
An arrangement according to the invention is characterized essentially in that the implant is provided with a first socket which can be assigned to the tool and a second socket geometrically separate from the first socket for receiving and rotationally locking the spacer element.
In further developments of the arrangement, it is proposed that a relatively high force applied by means of the tool on the first socket is prevented from mechanically affecting the second socket. The first socket can be arranged to meet a relatively high force application which can occur when the implant is screwed into the bone/jawbone despite small dimensions of the implant on account of the fact that the socket is internal. The second socket can be arranged to meet a relatively small force application which arises when the spacer element is applied, but can nevertheless operate with a precise positioning function.
A method according to the invention is characterized essentially in that the screwing-in is effected by means of a tool which is arranged on a tool socket provided in the implant and in that the spacer element is applied to a spacer element socket provided in the implant and separate from the tool socket.
Further developments of the method are characterized by the fact that a tool of star screwdriver type is arranged on an internal tool socket where, during screwing-in, the wing-shaped parts of the tool are pressed against essentially radially extending drive surfaces of the tool socket. The method also entails that conventional and well proven types of spacer elements can be applied to the spacer sockets of the implant in question.
By means of what has been described above, it is no longer necessary to integrate the tool and spacer element sockets. These can each be made optimal and by means of the geometrical separation it is possible to ensure that application of force which has been effected in the tool socket does not mechanically affect or destroy the spacer element socket, which can therefore instead be used for precise positioning of the spacer element. An undamaged spacer element socket also contributes to a fully satisfactory implantation result. There is therefore no risk of the spacer socket being damaged and of the work of implantation and healing having to be repeated. The tool socket can be designed in a manner known per se, see specifications cited above, to permit simple bearing of the implant by means of the screwing tool (bore machine) used. The tool can be manufactured to meet high precision demands, which is economically defensible since the tool can be used for a very large number of implant fittings.